1. Field of the Invention
The present invention relates to an array microphone having a plurality of microphone units arranged to form a microphone array.
2. Description of the Prior Art
An array microphone which has an enhanced directional characteristic, has widely been employed for remote recording with a high S/N ratio and for acoustic feedback suppression or elimination of howl effects generated by a loudspeaker system.
Such a known array microphone comprises a microphone array consisting of a plurality of microphone units, a plurality of delay circuits for delaying output signals of the respective microphone units, a plurality of signal amplifier circuits for weighting outputs of the respective delay circuits, and an adder circuit for summing outputs of the amplifier circuits. The output of the adder circuit is an output of the array microphone.
In the prior art array microphone, the direction of sound recording is controlled by the delay circuits and the output of each microphone unit is weighted by the corresponding signal amplifier circuit. This serves as a spatial filter for controlling the directional characteristic such that the main lobe is directed in a desired direction.
This type of directional characteristic has a nature of frequency dependence, i.e. it will be sharp when the frequency is high. Therefore, there is a disadvantage in that slight movement of a speaker during recording causes a great change in the sound quality. In a conventional method of sound recording with a moving speaker, a plurality of line microphones oriented in different directions are selectively switched according to the movement of the speaker or the direction of each line microphone is mechanically controlled. However, such manners require bulky and complicated hardware and are thus less practical. On the other hand, the conventional directional microphone has a fixed directional characteristic which is not adjustable to a desired directional characteristic for specific use and thus must be utilized in combination with different types of microphones including uni-directional types, bi-directional types, etc.